I can only echo Bill's comments.
Let's play devil's advocate, though. My concern is always what happens when the actor turns and talks to someone else. At that point, if they're both standing behind the counter, one of them is being blasted in the face, and one unattractively backlit. Typically one ends up cheating these things, so that the blastee is more sidelit by softer light than is strictly accurate, and so that the backlit character is getting more bounce and sidelight than she really would.
But this becomes even more difficult when the scene involves, say, a group of heavily-armed ninja dropping through the skylight, at which point our heroine vaults the counter and engages in melee combat with people who aren't really even covered by the original setup. What then?
The more movement there is in a scene, and the larger an area over which it occurs, the more difficult things become. One ends up duplicating the setup on, effectively, a larger and larger scale, and thanks to the inverse square law (and even more so for soft sources) the required amount of equipment and people increases, literally, exponentially.
I suppose this is why movies of the week are basically talking heads.